In the automated production of two- or multi-dimensionally bent parts with the aid of numerically controlled bending machines, the movements of machine axes in a bending machine are activated in a coordinated manner with the aid of a control device to generate one or more permanent bends on the workpiece, for example, a wire, tube, conduit or bar, by plastic forming. In a bending process, in this case, at least one portion of the workpiece is moved into an initial position in the engagement region of a bending tool by one or more feed operations, such as drawing in, positioning and/or orientation, and is formed in at least one bending operation with the aid of the bending tool.
When a bend is made in a bending operation, the free end of the bent part, which, where appropriate, is already bent once or more than once, is led around part of the bending tool, for example, a stationary bending mandrel. Particularly during the bending operation, but, where appropriate, also during the positioning of the workpiece and/or in the event of a change of the bending plane, the free end portion of the workpiece may be exposed to movements and accelerations which may lead to oscillations of the free end portion. This effect when oscillating movements of free workpiece portions are generated in the bending process is sometimes designated as the “whiplash effect.”
The whiplash effect usually has an adverse influence upon the production rate. Oscillatory movements may even cause undesirable plastic deformations on the bent part. The size, length and consequently the mass or mass inertia of the workpiece and also its rigidity have in this case a decisive influence upon the extent and nature of the undesirable oscillatory movements.
If problems with oscillations of the bent part occur or are expected, the speeds and/or accelerations of the machine axes in the event of oscillation-critical movements are usually reduced to an extent such that oscillations arise only to a non-disturbing extent or, ideally, will no longer arise at all. However, this way of limiting the causes has an adverse effect upon the production rate, since the part is bent more slowly. Alternatively or additionally, steadying times are sometimes programmed between the individual movements so that the oscillations of the already finished portion of the bent part can fade away to an acceptable value before a subsequent workstep of the manufacturing process is carried out. These possibilities for influencing the oscillation behaviour are based on the user's knowledge and ability and presuppose very experienced machine operators. In any event, the production rate of the bending machine is limited by these measures, and therefore, ultimately, the production costs of the bent parts rise.
Furthermore, table tops or other supporting elements are often used to limit the degrees of freedom of the oscillations and/or to damp them by friction. However, such measures require additional outlay in mechanical terms and frequently undesirably restrict bending clearance. Moreover, these are often solutions which are specific to a particular bent part and have to be redeveloped for each bent part or for a group of bent parts. The production costs of the bent parts also rise as a result.
It could therefore be helpful to provide methods and apparatus for the production of bent parts in which the adverse influence of oscillatory movements on the bent part is reduced considerably as compared to conventional methods and apparatuses. It could also be helpful to increase the production rate of bending machines or of the bending process.